The present invention relates to a method and installation for distributing sheets, especially glued together sheets such as paper, cardboard, corrugated paper and the like, where small sheet piles are formed and, after a predetermined number of small sheet piles, a specific number of small sheet piles is turned over back-to-front in a turning station for stacking of individual sheets at a final station.
Particularly with sheets which have been glued together, and which thus consist of different layers, it generally must be borne in mind that the sheets are internally stressed and therefore may buckle due to different initial levels of moisture. With a given combination of materials, the buckling always occurs toward the same side, and when the sheets are laid down in a pile the buckling becomes increasingly noticeable as the height of the pile increases. Mutual adaptations of the levels of moisture of the individual materials can be achieved before they are glued together only with considerable technical outlay and with relatively high energy consumption, both of which are costly. In prior art apparatuses, the glued sheets are gathered together in small piles which are then piled on top of each other so that every second pile is turned back-to-front. In this way the buckled sheets are flattened by the inherent weight of the sheets lying on top of them. When the gluing process has been completed, there then remains virtually no significant buckling.
It is known to perform the turning over of every second small pile by hand or mechanically, and to stack the small piles on a pallet to form a large pile. Turning over by hand is exacting work and the cost for doing so are high. Further, considerable disadvantages also exist in mechanically turning over the piles; namely, it is difficult to push the small piles which are still relatively heavy onto the final pile and to stack them in precise alignment. The technical outlay to perform this is considerable and, in addition, displacement may occur within the small piles during turning and transportation, which cannot be remedied later without considerable technical outlay.
Attempts have been made to solve the problem by distributing the sheets alternately by using two feeders on two sides, having previously turned the sheets of one of the feeders. However, such apparatuses are extremely expensive to build, and take up a great deal of space. Consequently, it is not possible to produce a coherent, compact plant from production machinery to the final stacking station. Further, since the times which elapse between production and the alternate turning over are relatively long, the buckling of the sheets has already been "frozen in" to a large extent and may no longer be remedied.
The present invention provides a method and an installation for carrying out the method by means of which it is possible to achieve, even in high output plants, substantially trouble free distribution of sheets already stacked in small piles, with the desired alternation of turned and unturned small piles, and which also may be used to establish a coherent, compact plant from production machinery to the final stacking station.
The present invention solves the above problem by providing a method wherein, between the turning station and final stacking station, the small sheet piles are arranged in a line of staggering, overlapping sheets, which is then subsequently delivered to the final stacking station, for example, a layboy. Preferably, the overlapping and staggering of individual sheets are effected from individual small sheet piles by moving the bottommost sheet in turn on the conveyor belt.
The method of the present invention makes possible the fully automatic, flawless stacking of the sheets in the desired alternating fashion which counteracts the buckling of the sheets, even in high output plants.
In a preferred embodiment for performing the method, according to the present invention, there is a device for staggering and overlapping sheets by means of an endless conveyor belt which acts on a pile from below and cooperates with a backup rail. The upper section of the conveyor belt, which is guided over a front guide roller and a rear guide roller, is passed back over a first deflection roller serving as a feed roller to form a conveyor belt loop out of the conveying plane and down over second and third deflection rollers into the original conveying direction again. Between the first and third deflection rollers, there is a slot which can be bridged by a sheet, and the upper surface of the feed roller projects beyond a tangential plane disposed on the surface of the rear guide roller and the surface of the third deflection roller. The backup rail is arranged in the conveying direction a predetermined distance from the loop in the conveyor belt. Preferably, the outlet slot formed between the backup rail and the conveyor belt is adjustable.
Such an installation according to the present invention could be arranged in a corrugated cardboard laminating machine adjoining a sheet collecting station and a turnover machine following it. In the sheet collecting station, the sheets which, after leaving the laminating machine, have been severed in a separating device and undergone a first sheet staggering and overlapping process, are gathered into small piles. Every second one of these small piles is turned over by the turnover device. All of the small piles are then staggered and overlapped again into a line of staggering and overlapping sheets so that individual sheets are supplied for stacking at the final station. In a known manner, side and end vibrators may be provided to push each top sheet into the correct position so that a smooth, aligned final pile is obtained. Accordingly, an ordinary layboy may be used.
According to an advantageous feature of the present invention, the installation is adaptable to different sheet format lengths. The deflection rollers for the upper section of the conveyor belt may be mounted in a longitudinally adjustable carriage, thereby making it possible to set the conveyor belt loop at the optimum distance from the backup rail for the format length involved in each particular case.
Another advantageous feature of the present invention permits variation in the size of the outlet slot formed between the conveyor belt and the backup rail, which is pivotable about an axis extending parallel to the conveyor belt and transverse to the conveying direction. Thus, control of the size of the opening of the outlet slot is simply accomplished, and is preferably effected by means of a cam disc that is preferably driven from the conveyor belt drive and engaged by a clutch. Another aspect of the invention permits the clutch to be released or tripped by a pulse transmitter having no contacts, for example, a photoelectric cell, which can be controlled by a small pile approaching the backup rail. In the basic position, the outlet slot is closed. The approach of a small pile is registered by the photoelectric cell and relayed to a control which starts the drive of a cam disc. By the time the bottom sheet has reached the backup rail, the outlet slot has been opened by an amount corresponding to the thickness of a sheet allowing the lowermost sheet to pass therethrough without impediment, while topmost sheets are held back by the backup rail. When this occurs, the small pile is essentially supported by a supporting table, which is disposed underneath the conveyor belt in the region of the backup rail, and by the feed roller. The feeding force for the bottom sheet is produced by the difference between the static friction of the sheet on the conveyor belt and the static friction between the sheets, the latter being substantially less. After the bottommost sheet has run forward a specified distance, the next sheet is pressed onto the feed roller and experiences a feeding force increased by the sliding friction between the sheet and the conveyor belt with half the weight of the pile. Meanwhile, the outlet slot has been increased by a further sheet thickness so that the second sheet may pass therethrough.
Since the cam disc is driven by the conveyor belt drive, the overlapping and staggering of sheets is fixed and dependent upon specific sheet thicknesses, irrespective of the format length of the sheets. This fixed amount of overlapping and staggering can be varied by changing the transmission ratio of the drive.
When the trailing edge of the first or bottommost sheet has passed the backup rail, the outlet slot is not enlarged again. This is accomplished in accordance with the invention by providing a time relay which can control the maximum opening of the outlet slot. The time relay may also switch the drive off. Everytime a trailing edge of the sheet passes through the outlet slot, the leading edge of the following sheet is urged on by the weight resting on top of it. The overlapping and staggering of sheets is maintained without the outlet slot being enlarged any further. When the last sheet has passed through the outlet slot, this is reported by the photoelectric cell to the control and the backup rail moves back into its basic position to close the outlet slot.
It is an object of the present invention to provide an improved method for the distribution of sheets, especially glued together sheets such as paper, cardboard, corrugated cardboard and the like.
Another object of the present invention is to provide an installation for performing the method.